Relation of open circuit voltage to charge carrier density in organic bulk heterojunction solar cells

摘要

The open circuit voltage V_(oc) and the corresponding charge carrier density were measured in dependence of temperature and illumination intensity by current-voltage and charge extraction measurements for poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C_(61) butyric acid methyl ester (PCBM) and P3HT:bisPCBM solar cells. At lower temperatures a saturation of V_(oc) was observed which can be explained by energetic barriers at the contacts (metal-insulator-metal model). Such injection barriers can also influence V_(oc) at room temperature and limit the performance of the working solar cell, as was assured by macroscopic device simulations on temperature dependent IV characteristics. However, under most conditions—room temperature and low barriers—V_(oc) is given by the effective band gap.